The following commit has been merged into the sched/core branch of tip: Commit-ID: c1cecf884ad748f63f9139d5a18ee265ee2f70fb Gitweb: https://git.kernel.org/tip/c1cecf884ad748f63f9139d5a18ee265ee2f70fb Author: Sebastian Andrzej Siewior <bige...@linutronix.de> AuthorDate: Wed, 19 Aug 2020 22:00:25 +02:00 Committer: Peter Zijlstra <pet...@infradead.org> CommitterDate: Wed, 26 Aug 2020 12:41:58 +02:00
sched: Cache task_struct::flags in sched_submit_work() sched_submit_work() is considered to be a hot path. The preempt_disable() instruction is a compiler barrier and forces the compiler to load task_struct::flags for the second comparison. By using a local variable, the compiler can load the value once and keep it in a register for the second comparison. Verified on x86-64 with gcc-10. Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Link: https://lkml.kernel.org/r/20200819200025.lqvmyefqnbok5...@linutronix.de --- kernel/sched/core.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8471a0f..c36dc1a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4551,9 +4551,12 @@ void __noreturn do_task_dead(void) static inline void sched_submit_work(struct task_struct *tsk) { + unsigned int task_flags; + if (!tsk->state) return; + task_flags = tsk->flags; /* * If a worker went to sleep, notify and ask workqueue whether * it wants to wake up a task to maintain concurrency. @@ -4562,9 +4565,9 @@ static inline void sched_submit_work(struct task_struct *tsk) * in the possible wakeup of a kworker and because wq_worker_sleeping() * requires it. */ - if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) { + if (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) { preempt_disable(); - if (tsk->flags & PF_WQ_WORKER) + if (task_flags & PF_WQ_WORKER) wq_worker_sleeping(tsk); else io_wq_worker_sleeping(tsk);
